With the growing demand for wireless services, Radio Frequency (RF) circuits become more and more versatile. For example, the number of wireless access technologies and the frequency range in which mobile communication systems are active are growing, wherein a physical size and power consumption of RF units is decreasing. For example, 5th Generation (5G) systems may operate using mm-wave technology, e.g. the U.S. Federal Communications Commission (FCC) approved spectrum for 5G, including the 28, 37, and 39 GHz bands.
The FCC also released a Report and Order on Apr. 17, 2015 outlining the rules for operating wireless devices in the 3.5 GHz band that spans from 3550-3700 MHz. FCC released this spectrum for sharing with incumbents. The incumbents (mainly DoD, Department of Defense) get priority in that band and it can be used by broadband devices when (and where) incumbents are not using the spectrum. There are two additional tiers of spectrum users in addition to the incumbents namely the Priority Access (PA) and General Authorized Access (GAA) users. The Priority Access Licenses (PAL) users get protection from GAA users, which is similar to unlicensed spectrum.
The FCC also mandates a Spectrum Access System (SAS) that will coordinate the spectrum use between the incumbents, PAL and GAA users. The SAS is central to this band, and no tier 2 or tier 3 device can operate unless it is in constant communication with the SAS and receives information of when and where to use the 3.5 GHz channels. The SAS has to be approved by the FCC before it can be deployed. Since the SAS is the central coordinator for this spectrum, it needs to have a lot of information about the network and devices. In fact, FCC mandates most of this information to be contained in the SAS. FCC's Report and Order outlines a sample system with SAS(s). If there are multiple SASs, they are supposed to be synchronized with each other. However, the FCC does not specify details of how the SAS have to be implemented and what information has to be synchronized.
In Europe a Licensed Shared Access (LSA) concept has been proposed in which a first tier supports incumbent users and a second tier supports licensee users, e.g. at 2.3-2.4 GHz (cf. Long Term Evolution Band 40). Incumbents are protected using a data base at an LSA controller controlling the second tier access nodes.
Spectrum management entities like SAS (3.5 GHz in USA) or LSA (2.3 GHz in EU) are new entities that are now part of the wireless communications network. SAS and LSA concepts are not limited to a certain frequency band and may also be applied to any other frequency band, typically between 0 Hz and 1 THz. The SAS system is also known as Citizen Broadband Radio Service (CBRS).